Excel 2003 is limited to 65,536 rows. Therefore, if your school has more than 65,536 rows of data, you will not be able to open or save that data set in Excel. If you have multiple zip codes that will result in more than 65,536 rows of data you can create two separate files. Split your zip codes into two groups and then access them separately.
that why selecting one zip code at time gets you more matched .